Many novel laser cavity designs have been developed for optically exciting a solid state gain medium to produce a laser cavity output beam. For example, in a side-pumped laser cavity design, one or more pump sources (e.g. flash lamps, laser diodes, etc.) are placed along the length of the gain medium. The gain medium is therefore optically pumped perpendicular to the direction of propagation of the intracavity laser beam. Thus, during a single round trip through the cavity, the laser beam passes through and is amplified by the gain medium once in a ring cavity configuration, or twice in a transverse cavity configuration. This geometry is advantageous because multiple pump sources can be positioned along the gain medium's length, thus increasing laser mode amplification. However, side-pumped laser cavity configurations suffer from low conversion efficiencies and low beam quality.
In an end-pumped laser cavity design, the output from the pump source is focused into the entry or exit face of the gain medium co-linearly with the intracavity laser beam. The gain medium is therefore optically pumped parallel to the direction of propagation of the intracavity laser beam. This design has good conversion efficiency and mode quality. However, end-pumped laser designs require special optical elements to separate the pump power radiation from the laser beam. Further, it is difficult to focus the output from a plurality of pump sources through the entry and exit faces of the gain medium, let alone maintain proper alignment.
The output power of end-pumped laser cavity designs has been increased by using special cavity or gain medium geometries that allow multiple pump sources to co-linearly excite the gain medium. U.S. Pat. No. 5,170,406 discloses placing a plurality of pump sources circumferentially about the gain medium optical axis with the pump beams directed into the end faces of the gain medium at relatively small multiplexing angles to the optical axis. U.S. Pat. No. Re 34,729 discloses dichroic mirrors on opposite sides of the gain medium through which multiple pump sources excite the gain medium. The beam travels through the gain medium in a zig-zag pattern between the dichroic mirrors, thus providing several optimal entry points for pump beams to optically pump the gain medium. U.S. Pat. No. 5,148,441 discloses arranging laser medium pellets to correspond to a zigzag reflected beam pattern.
The above described cavity geometries have several drawbacks. Specifically, these cavity designs are complex, are difficult to align and to maintain alignment, are exceedingly large, exhibit adverse thermal lensing, are difficult to reliably control the laser mode, require special optics to separate pump power from the laser beam, and are difficult to provide adequate cooling to the gain medium and all the pump sources.
There is a need for a simplified, easy to align solid state laser cavity that minimizes adverse thermal lensing, takes up minimal space, and provides adequate cooling for both the gain medium and all pump sources.